Surely it can only drag its tail when on the gound? Unless it had a severe CofG problem that I’m unaware of?

CofG problems! On occasions, the Shack II had a propensity to drag its tail when in the air, too. I recall several (four?) a/c on 224 Sqdn having to be stripped bare of the fancy paint job that had been added to their aft fuselage and tail for a tour of South America, as the trim was seriously affected by the several coats of paint in these areas i.e. original (possibly more than one coat), South America scheme, repaint back to standard. This extra weight had trim implications too;(throw several buckets of the finest sea grey ‘dulux’ on the scales to find out how heavy this was when spread all over the rear end of the grey lady:D).
The Shackleton tailwheel was also well-known for cocking sideways at times during the takeoff run; this provided much amusement to onlookers as various attempts were made to bump it into a more regular alignment.